As a method for producing dialkylhydroperoxybenzene by subjecting an oxidation raw material solution containing dialkylbenzene to oxidation reaction, a method for producing 1,3-di-(2-hydroperoxy-2-propyl)benzene is disclosed, for example, in unexamined Japanese Patent Publication No. 2002-322146 as a typical example. In this method, in addition to 1,3-di-(2-hydroperoxy-2-propyl)benzene (hereinafter, referred to as DHPO), the oxidation reaction liquid contains 3-(2-hydroxy-2-propyl)-1-(2-hydroperoxy-2-propyl)benzene (hereinafter, referred to as CHPO), 3-isopropyl-1-(2-hydroperoxy-2-propyl)benzene (hereinafter, referred to MHPO), unreacted 1,3-diisopropylbenzene (hereinafter, referred to MDC), and by-produced 1,3-di-(2-hydroxy-2-propyl)benzene (hereinafter, referred to as DCA). The oxidation reaction liquid is subjected to extraction using an alkali aqueous solution such as a sodium hydroxide aqueous solution so as to obtain a water layer mainly containing DHPO and CHPO and an oil layer mainly containing MHPO, MDC, and DCA. A part of the oil layer is ordinarily recycled and fed to an oxidation step as a recycled oil in order to recover MHPO and MDC. However, in a conventional technique, the recycled oil contains an extracting agent component such as alkali used in the aqueous solution extracting step, and this alkaline component is fed to the oxidation step with the recycled oil. The alkaline component promotes generations of CHPO and DCA, and reduces a generation of DHPO in the oxidation step. Thus, the yield of DHPO is hardly improved.
Further, the above-described method cannot increase the amount of the recycled oil, and thus cannot keep high MDC concentration in a raw material to be recycled.
Furthermore, Unexamined Japanese Patent Publication No. S59-82327 discloses a technique in which the alkaline component in the recycled oil is washed so as to control pH in an oxidation reactor. However, since pH in the oxidation reactor is kept within the range of 7 to 7.5 in this technique, the amount of the recycled oil cannot be increased. Thus, this technique cannot keep high MDC concentration in a raw material to be recycled.